Cathode ray apparatus



Jan. 22, 1935. v, ZWORYKIN T AL 1,988,469

CATHODE RAY APPARATUS Filed June 30, 1931 INVENTOR. Vladimir K.Z.wo-r'g Kin,

JohnCBcflZcheloT? T IE ATTORNEY.

Patented Jan. 22, 1935 UNITED STATES PATENT OFFICE Batchelor, Edgewater Park, N. J., ass! gnors to Radio Corporation of America, a corporation of Delaware Application June 30, 1931, Serial No. 547,904

18 Claims.

Our invention relates to improvements in cathode ray apparatus and methods of manufacturing the same.

In the use of cathode ray tubes proposed heretofore for television reception, wherein the image is developed on a fluorescent screen by causing a cathode ray to scan the same, it has been necessary to maintain the normal intensity of the ray at an undesirably high value in order to obtain a satisfactory degree of contrast of the image. The cause for this can be attributedto the fact that when a sufficiently brilliant image is formed on the fluorescent screen, part of the light emitted therefrom is radiated inwardly and reflected back to the screen from light-reflective structure forming part of the tube, such as the wall of the tube and the metal parts comprising the electron gun. When the tube is made out of glass and, particularly, when it is metalized to provide a ray- '20 focusing anode in the form of a bright metal coating, the wall of the tube reflects a relatively great amount of this inwardly-radiated light, from the screen, back to the same. A background of appreciable brilliancy is thereby created which has the effect of decreasing the contrast of the the image unless the intensity of the cathode ray is maintained, as heretofore, at an undesirably high value to offset this optical efiect.

One of the objects of our invention, therefore, is the provision of improved cathode ray apparatus of the character referred to with which satisfactory contrast of the image can be obtained with a ray intensity substantially lower than has been possible with the various constructions proposed heretofore.

Another object is to obtain the advantage referred to in a simple and inexpensive way without interfering with the process of evacuation of 40 the apparatus at high temperatures, and without diminishing the efliciency of the fluorescent screen.

Other objects and advantages will hereinafter appear.

For the purpose of illustrating our invention, an embodiment thereof is shown in the drawing, wherein a Fig. 1 is an elevational view, partly in section,

of cathode ray apparatus constructed in accordance with our invention;

Fig. 2 is an elevational, sectional view, illustrating a step in our improved method of manufacturing cathode ray apparatus; and

Fig. 3 is an enlarged fragmentary view, taken from Fig. 1.

In accordance with our invention, certain of the structure forming part of cathode ray apparatus is made substantially non-reflective to light emitted, incidental to operation of the apparatus, from other structure. also forming 5 part of the apparatus.

Further, in accordance with our invention, wall structure of cathode ray apparatus which would otherwise be reflective to light emitted from the usual fluorescent screen, is made non-reflective. 10

More particularly, in accordance with our invention, the wall structure referred to is covered with carbonaceous material, and the cathode ray apparatus is subsequently evacuated at a temperature substantially of the order of five hundred 15 degrees centigrade.

Our invention resides in the construction and the method of manufacturing cathode ray apparatus of the character hereinafter described.

In Fig. 1 is shown cathode ray apparatus of the general type disclosed in the copending application of Vladimir K. Zworykin, Serial No. 407,652, filed November 16, 1929, and assigned to the Westinghouse Electric and Manufacturing Co. This apparatus includes the usual evacuated glass tube or containing vessel 10, sealed-01f at 10a, and provided at one end with suitable fluorescent screen structure 11 and at the other end with a suitable electron gun 12 for generating a cathode ray 13 and directing the same toward the screen structure which functions as a target therefor.

The wall structure 14 of the tube is metallized to provide a ray-focusing anode in the form of a bright silver coating 15.

Ordinarily, when a brilliant image is formed on the screen 11, part of the light emitted is radiated inwardly and would be reflected back to the screen from the bright metal coating 15 and the bright metal parts comprising the electron gun 12. This reflecting action is believed to take place, in the cathode ray apparatus constructed heretofore, in some such fashion as indicated by the arrow-headed broken lines 16, 17, and 18. For example, some of the light radiated inwardly from a spot 19 on the screen would be reflected back to a spot 20 from the wall structure 14 along the path 16. Similarly, some of the light from a spot 21 would be reflected back to a spot 22 along the path 17. Some of the light from a spot 23 would be. reflected back to a spot 24 60 from the bright metal parts comprising the electron gun, along the path 18.

This reflecting action causes, in cathode ray apparatus constructed heretofore, a background on the screen which decreases the contrast of the image unless, as explained, the normal ray intensity is maintained at an undesirably high value.

In our improved construction, however, the

structure from which light would otherwise be reflected back to the screen 11 is made completely non-reflective with the result, as has been found, that with a ray intensity of about one-fourth the ray-intensity heretofore employed, the same degree of satisfactory contrast of the image is obtained. The means and methods for doing this will now be explained.v

A solution of colloidal carbon is placed in the tube 10 and the latter is tilted, as shown in Fig. 2, and slowly rotated about its longitudinal axis 26 until the bright surface of the metal anode 15, previously formed in situ, has been covered with the solution. During this step, the open neck of the tube is closed by a suitable stopper 2'? or by the hand. The excess liquid is then allowed to drain, leaving a black film or coating 28 of carbonaceous material over the entire surface of the metal coating 15.

The strength. of the solution of colloidal carbon is such that the black film 28 is sufiiciently thick to be substantially non-reflective, yet thin enough not to produce excessive gas when heated in a vacuum at temperatures of the order of five hundred degrees centigrade. For this purpose, a ten per cent solution of the so-called commercial "Acheson Aquadag in distilled water was found to be satisfactory.

The carbon deposited on the neck of the tube is wiped off to the edge 29 of the metal coating 15, since, apparently, there is no undesirable reflection from this surface and the carbon, if left on the same, might produce some gas to unnecessarily prolong the time required for evacuation of the tube. v

The bright surfaces of the metal parts comprising the electron gun 12 are also coated with carbon by dipping these parts in the colloidal solution referred to. The coated gun is. then degasified in a vacuum before being introduced into the neck of the tube 10.

It also is within the scope of our invention to make the bright surface of the metal coating 15 non-reflective by forming a black chemical compound with the metal. For example, when the coating 15 is silver, the same may be exposed, at elevated temperatures, to hydrogen sulphide gas to form a black film of silver sulphide, Hydrogen selenide gas may also be used, in like manner, to form a black film of silver selenide. Also, a silver selenide film may be formed by washing the bright silver coating 15 with a saturated solution of selenium in carbon disulphide. draining off the excess solution, and washing the silver selenide film formed with a suitable solvent to prevent further reaction.

The silver coating, also, may be treated with a solution of tellurium, hydrogen telluride gas, or tellurium vapor to' form a black film of silver telluride. 1

We believe ourselves to be the first to provide cathode ray apparatus comprising an evacuated, sealed-off glass tube, and characterized by the fact that certain of the structure forming part of the apparatusis substantially non-reflective to light emitted from other structure of the apparatus during normal operation thereof, and which would otherwise be reflected back to the second structure from the first structure to cause an undesirable optical eifect.

We claim as our invention:

1. Cathode ray apparatus comprising a containing vessel provided with screen structure and with means for developing a cathode ray and directing the same toward said structure, the sur- 5 face of said means exposed to said screen structure being substantially non-reflective to light emitted from said structure incidental to operation of said apparatus.

'2. Cathode ray apparatus comprising a containing vessel provided with screen structure and with means for developing a cathode ray and d!" recting the same toward said structure, and electrode structure interposed between said means and said screen structure, said apparatus characterized by the fact that the surface of said electrode structure is substantially non-reflective to light emitted from said screen structure incidental to operation of said apparatus.

3. Cathode ray apparatus comprising a containing vessel provided with screen structure and with means for developing a cathode ray and directing the same toward said structure, the wall structure of said apparatus being provided with a rayfocusing electrode in the form of a metallic coating thereon, said coating being substantially nonreflective to light emitted from said screen structure incidental to operation of said apparatus.

4. Cathode ray apparatus comprising an evacuated sealed-off glass tube provided with fluorescent screen structure and with an electrode in the form of a. metallic coating on the wall of the tube, and means for developing a cathode ray and directing the same toward said structure, the surface of said coating being substantially non-reflective to light emitted from said screen structure during normal operation of said apparatus.

5. Cathode ray apparatus comprising a containing vessel provided with screen structure, means for developing a cathode ray and directing the same toward said structure, and an electrode for focusing the ray on said structure, said electrode having a surface coating in the form of a chemical compound substantially non-reflective to light emitted from said screen structure incidental to operation of said apparatus.

6. Cathode ray apparatus comprising a tube provided with fluorescent screen structure, and means for developing a cathode ray and directing the same at saidscreen structure, at least part of the surfaces of.said apparatus being substantially non-reflective to light emitted from said screen structure during normal operation of said apparatus.

7. In combination, a container having a wallportion permeable to light, a target within the container visible through said portion and an electron gun disposed within the container in spaced relation to the target and directed thereat for subjecting the target to electronic bombardment, the major portion of the inner surface of the container, exclusive of the light-permeable portion, being light absorbent whereby light emitted by or reflected from the target during operation of the device is in large measure prevented from again reaching the target.

8. The invention set forth in claim "I, characterized in that the said major portion of the inner surface of the container carries a layer of nonreflective material.

9. The invention set forth in claim 7, characterized in that the said mador portion of the inner surface of the container carries a layer of finely divided carbon.

10. The invention set forth in claim '1, chartarget within the container, an electron gun disposed within the container in spaced relation to the target and directed thereat for subjecting the target to electronic bombardment, and an electron-focusing electrode, through which electrons may pass, disposed between the electron gun and the target, the surface of said electrode exposed to the target being light absorbent whereby light emitted by or reflected from the target during operation of the device is in large measure prevented from again reaching the target.

12. The invention set forth in claim 11, characterized in that the focusing electrode is rendered light-absorbent by a layer of finely divided carbon thereon.

13. The invention set forth in claim 11, characterized in that the focusing electrode is rendered light-absorbent by a surface layer of a chemical compound formed in situ.

14. The invention set forth in claim 11,, characterized in that the focusing electrode is silver and is provided with a surface layer or a silver compound from the group comprising only silver sulphides, silver selenides and silver tellurides.

15. In combination, a container in which is disposed a target, an electron gun disposed within the container and directed toward the target whereby the said target may be subjected to electronic bombardment and means also within the container for preventing light emitted by or' reflected from the target, when under bombardment, from being reflected back onto it from the electron gun.

16. The invention set forth in claim 15, characterized in that the last named means is constituted by a light-absorbent coating disposed on the surfaces of the electron gun visible from the target.

17. The invention set forth in claim 15, characterized in that the last named means is constituted. by a coating of flnely divided carbon disposed on the surfaces of the electron gun visible from the target. g 4

18. In combination, a container, a target disposed within the container. an electron gun having light-absorbent surfaces disposed within the container in spaced relation to the target and directed thereat for subjecting the target to electronic bombardment, and an electron-focusing electrode, through which electrons may pass, in-

terposed between the electron gun and the target,

the surfaces of the said electrode also being lightabsorbent, whereby light emitted by or reflected from the target is prevented in large measure from again reaching the target.

VLADIMIR Ki ZWORYKIN. JOHN C. BATCHELOR.

Certificate of Correction Patent No. 1,988,469 January 22, 1935 VLADIMIR K. ZWORYKIN ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Page 2, second column, lines 15 and 16, strike out "said apparatus characterized by the fact that; line 17, for the word is read being;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 4th day of April, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

